If you’re like many investors, you might be thinking it’s time to take some risk off the table.

On Wednesday, barring a crash, this bull market will become the longest in the history of the S&P 500, according to S&P Dow Jones Indices. Stocks have been rising steadily, without the 20% decline that conventionally defines a bear market, since March 2009—making this bull run about to exceed the nearly-10-year stretch that ended in March 2000.…